نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 63 (زمستان 1401)

In this study, effects of alumina nanoparticles and stirring pass in mechanical behavior of friction stir welded AM60 magnesium alloy were studied. Microscopic analysis showed occurrence of dynamic recrystallization during plastic deformation in weld area and mechanical tests revealed optimum condition for hardness and tensile strength could be produced in 1200 rpm rotational speed not only in absence of reinforcing alumina nanoparticles but also in presence of them. Opposing effects of higher temperatures in grain growth and greater strains in lowering grain size should be considered. In lacking of alumina nanoparticles, grain size diminished with increasing stirring pass but in being nanoparticles, predominant mechanism in depressing grain size came from nanoparticles and negligible effect of stirring pass in grain size was found. XRD results showed increasing solubility of γ-Mg phase as a result of stirring operation. Better toughness performance of weldment was produced via decreasing size of agglomerated alumina particles. Higher hardness and greater ultimate tensile strength were achieved in specimens with alumina nanoparticle with increasing rotational speed. In a constant rotational speed, higher hardness and greater ultimate tensile strength achieved in samples having alumina nanoparticles in contrast with free alumina nanoparticle samples

Zn-based alloys (Zn) with control of the production process have the potential to give rise to a wide range of properties required for use in short-term implants. For this purpose, in the present study, a Zn-4wt%Mn alloy was prepared by mechanical alloying in three times of 10, 20 and 30 hours. Then some blocks were made by Spark plasma sintering (SPS) process. Heat treatment of manufactured parts was performed at three temperatures of 150, 200 and 250 ° C. The samples were characterized using XRD, dynamic polarization corrosion test and MTT cell viability evaluation. Also, the surface morphology of the samples was determined using scanning electron microscopy (SEM). The results showed that increasing the milling time to 30 hours created a more homogeneous composition, and the heat treated sample at 250 ° C had the highest corrosion resistance. Cell viability of the heat treated samples at this temperature showed higher viability than other samples. The results of this study are expected to be used in short-term implants.

In this research, the bonding of aluminum matrix nanocomposites reinforced by Al3V particles was investigated using a transient liquid phase of bonding process and evaluating its properties. The effect of temperature and time of bonding on the properties was also investigated. For this purpose, Al-Al3V nanocomposite components were first prepared for bonding. The copper metal was used as the intermediate layer and bonding of these components was investigated by the transient liquid phase method at 560, 580 and 600°C, and 20, 40 and 60 min. Scanning electron microscopy was used to evaluate the microstructure of the joint. The shear strength of the joints was also evaluated by a pressure test device. The results indicated better bonding at 580 and 600°C than other samples. With increasing bonding temperature, the melt volume increased at the bonding joint and thus a wider surface area is filled by melt. According to the microhardness results, the maximum hardness of the joint is at 600 ° C for 20 min due to the diffusion of copper and formation of Al2Cu precipitated particles around the joint seam. The maximum joint shear strength of 65 MPa was achieved at 600 ° C for 40 min.

In the present study, ZrB2 nano powders were synthesized using sol-gel method. Zirconium alkoxide was used as the source of zirconium and boric acid as the source of boron. The size of precursor nanoparticle was controlled using the pH parameter inside the sol, and the formation of primary nuclei of ZrB2 phase and their crystallized amount were investigated using the temperature parameter. To evaluate the mechanism of product formation during the sol-gel process, DLS analysis showed that the size of precursor particle inside the sol at pH less than 5 was below 10 nm. Mixing of precursor particles at molecular level inside the sol was one of the important reasons in reducing the synthesis temperature of ZrB2 particles. FTIR analysis on chemical bonds showed that Zr-O-B bond was formed inside the gel powder.DTA analysis showed that the primary nuclei of ZrB2 particles were formed at a temperature of about 1400 °C. XRD observations proved that the primary nuclei of the ZrB2 phase crystallized and grew at a temperature of about 1500°C. Surface research revealed that the specific surface area of the synthesized ZrB2 particles is equivalent to 115 m2/g, and also the surfaces of these particles are porous, and the size of these porosities is in meso range. SEM analysis showed that the particle size of ZrB2 having homogeneous morphology is about 50 nm. TEM microstructural analysis revealed that ZrB2 particles were formed uniformly and orderly in very fine dimensions.

The impact of hybrid organic/inorganic pigments based on the herbal extract of Echium amoenum and zinc acetate on the corrosion protection performance of epoxy ester coating was investigated in this paper. The electrochemical impedance spectroscopy (EIS) measurement showed that the presence of hybrid pigment can expressively prevent the corrosion of steel in saline solution. The results of scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), visible ultraviolet (UV-Vis) spectroscopy and static contact angle proved the formation of chelates and protective complexes in the pigment structure. The inhibition efficiency of 89.3% shows the same point. The low-frequency impedance value of epoxy coating increased in the absence and presence of the hybrid pigment from 344 MΩ cm2 to 6056MΩ cm2. This parameter was calculated after 45 days for the blank coating and the one containing pigment 4.2 MΩ cm2 and 200 MΩ cm2, respectively, which indicates the role of pigment in increasing the barrier performance of the coating. Increasing the overall resistance values equivalent to 16343 Ω.cm2 in the epoxy coating containing pigments with synthetic scratches shows the active inhibitory role of hybrid pigments.

By controlling the synthesis conditions, hematite particles with different geometric shapes and different optical and magnetic properties can be obtained. In this study, due to its high potential for the synthesis of a wide range of particles with different shapes and sizes, the hydrothermal method was used for the synthesis of hematite. Iron (III) hexahydrate, ethanol, sodium acetate, and polyethylene glycol were used as raw materials. In this study, without using common organic solvents and in contrast with most previous researches that focused on the magnetic properties of hematite, Samples were synthesized at 180 and 250 °C and pHs 5, 7, and 11. The phase composition, particle shape, and optical properties of the particles were investigated by XRD, SEM, FTIR, and DRS methods. Hematite particles synthesized at the temperature of 180 °C at pHs 5, 7, and 11 had particle dimensions 293.47, 95.41, and 83.95 nm and at the temperature of 250 °C at pHs 5, 7, and 11 had particle dimensions 88.29, 73.79, and 59.33 nm respectively. As the pH increased, due to the smaller particle size and thus more light absorption, the color of the hematite powder darkened. By using XRD analysis and Scherer equation, it was found that the pH of the process did not affect the size of the unit cells, and the average size of the unit cells at both synthesis temperatures was 27.8 nm. However, the SEM images showed that by increasing pH the hematite particles became more spherical and smaller.

In this study, Ta, TaC and TaSiC coatings have been deposited by a non-reactive magnetron sputtering method, and their structural, microstructural, mechanical, and corrosion properties have been investigated. XRD results revealed the presence of α-Ta and TaC0.6 phase structures in the Ta and TaC coatings, respectively. However, the TaSiC coating showed a quasi-amorphous structure. Additionally, the Ta coating showed a columnar microstructure with rough topography and tensile residual stress, while the addition of carbon and silicon resulted in the compactness and smoothness and domination compressive residual stress in the TaC and TaSiC coatings. Nanoindentation results showed that the addition of carbon to the Ta coating increased the hardness by four times, however the addition of silicon to the TaC coating had an adverse effect on the hardness of the coating. The corrosion studies revealed that the coatings have a cathodic nature with respect to the ST37 substrate, making the samples susceptible to galvanic corrosion. Furthermore, the addition of carbon and silicon was found to improve the corrosion resistance of the coatings by increasing the coating compactness and decreasing the density of open porosities.